Euthyrox® N 25: composition and pharmaceutical form
Euthyrox® N 25 is a tablet containing 25 micrograms of levothyroxine sodium. This is the lowest strength in the range: the medicine also comes as tablets of 50, 75, 88, 100, 112, 125, 137, 150, 175 and 200 micrograms.
Such a set of strengths is needed so that the dose can be fitted to the individual person while still managing with one tablet a day. The 25-microgram strength is most often used at the start of treatment and for the fine adjustment of the daily dose. The tablets contain lactose, so the medicine is not suitable for people with the rare hereditary galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption syndrome.
How Euthyrox® N 25 works
Synthetic levothyroxine acts in the same way as the natural main hormone produced by the thyroid gland. In the peripheral organs it is converted into triiodothyronine (T3) and, like the body's own hormone, exerts a specific action on the T3 receptors.
The body does not distinguish levothyroxine that has come from outside from its own. That is exactly why replacement therapy in hormone deficiency reproduces normal physiology, while an excessive dose gives a picture indistinguishable from hyperthyroidism.
Indications
Levothyroxine at a strength of 25 micrograms is prescribed in the treatment of non-toxic goitre, for the prevention of recurrence after the surgical removal of such a goitre — taking into account how much thyroid tissue has retained its function after the operation — and also as replacement therapy in hypothyroidism and suppressive therapy in thyroid cancer.
Another indication for the low strengths is as an addition to treatment with antithyroid agents in thyrotoxicosis: levothyroxine is added to the antithyroid medicines once the euthyroid state has been reached. Individual strengths of the medicine are also used in diagnostic tests of thyroid suppression.
Method of use and dosage
The whole daily dose is taken at once — in the morning on an empty stomach, half an hour before breakfast, with a small amount of liquid, for example half a glass of water. The figures given below are only a general guide: the individual daily dose is determined from the laboratory results and the clinical assessment. Since in many patients the T4 and free T4 levels are raised, a more reliable reference point is the baseline serum concentration of thyroid-stimulating hormone. Treatment starts with low doses and they are raised gradually, every 2–4 weeks, until the full replacement dose is reached.
| Situation | Daily dose of levothyroxine sodium |
|---|---|
| Treatment of non-toxic goitre | 75–200 micrograms |
| Prevention of recurrence after surgery for goitre | 75–200 micrograms |
| Replacement therapy in hypothyroidism in adults | Starting 25–50 micrograms, maintenance 100–200 micrograms |
| Suppressive therapy in thyroid cancer | 150–300 micrograms |
| Addition to antithyroid agents in thyrotoxicosis | 50–100 micrograms |
A cautious start and the length of treatment
In older people, in patients with ischaemic heart disease and in those with severe or long-standing hypothyroidism, treatment is started with particular caution: the starting dose may be 12.5 micrograms a day, it is raised in steps of 12.5 micrograms as well and at wide intervals — for example once every two weeks — with frequent monitoring of hormone levels. Sometimes one has to stop deliberately at a dose below the optimum, at which the TSH does not fully normalise. Practice shows that patients with a low body weight and a large nodular goitre need smaller doses. Newborns and infants with congenital hypothyroidism, where it is important to make good the deficiency quickly, are given 10–15 micrograms per kilogram of body weight a day for the first 3 months, after which the dose is adjusted individually. Replacement therapy in hypothyroidism, after removal of the gland and for the prevention of goitre recurrence is usually lifelong; in mild non-toxic goitre the treatment takes from 6 months to 2 years.
Contraindications
Euthyrox® N 25 is not prescribed in the following cases:
- hypersensitivity to levothyroxine or to any excipient;
- untreated adrenal insufficiency;
- untreated pituitary insufficiency;
- untreated thyrotoxicosis;
- recent myocardial infarction;
- myocarditis;
- acute inflammation of all the layers of the heart (pancarditis).
Special warnings and precautions
Before treatment with thyroid hormones is started, coronary insufficiency, angina pectoris, atherosclerosis of the vessels, arterial hypertension, pituitary and adrenal cortex insufficiency and autonomous thyroid function must be ruled out or treatment for them begun. If autonomous function is suspected, a thyroliberin test or suppression scintigraphy is carried out before treatment. In secondary hypothyroidism its cause is established first and, if necessary, replacement therapy for compensated adrenal insufficiency is begun.
- in patients with coronary insufficiency, heart failure and tachyarrhythmias even a slight drug-induced hyperthyroidism must not be allowed — the hormone level is monitored frequently;
- where there is a risk of psychotic disorders, treatment starts with low doses, is built up gradually and is watched closely; if psychotic symptoms appear, the dose is reviewed;
- in postmenopausal women with hypothyroidism and an increased risk of osteoporosis, levothyroxine concentrations above the physiological range are avoided and the thyroid function parameters are monitored carefully;
- in thyrotoxicosis levothyroxine is used only together with antithyroid agents — outside that situation it is contraindicated;
- when one levothyroxine preparation is replaced by another, the dose is adjusted according to the clinical response and the test results;
- concomitant use of orlistat can lead to hypothyroidism or worsen its control: the medicines are separated in time of day, the dose is sometimes changed, and thyroid function is monitored;
- patients with diabetes mellitus and those receiving anticoagulants need separate monitoring, the details of which are decided by the doctor.
No specific studies of the influence on the ability to drive and to operate machinery have been carried out. Since levothyroxine acts in the same way as the body's own thyroid hormone, no such influence is expected when it is taken as prescribed.
Drug interactions
Levothyroxine weakens the action of glucose-lowering medicines, so at the start of therapy blood glucose is monitored often and the doses of the antidiabetic agents changed if necessary. The action of anticoagulants, on the contrary, may be enhanced: levothyroxine displaces them from protein binding, and this raises the risk of bleeding, including into the central nervous system and from the gastrointestinal tract, especially in older people. At the start of treatment the clotting parameters are monitored regularly and the anticoagulant dose adjusted if necessary.
The absorption of levothyroxine is reduced by colestyramine and colestipol — the medicine is taken 4–5 hours before them — and also by agents containing aluminium (antacids, sucralfate), iron preparations and calcium carbonate, which are taken at least 2 hours after levothyroxine. Its action is also weakened by soya-containing products, sevelamer, tyrosine kinase inhibitors (imatinib, sunitinib), sertraline, chloroquine with proguanil, and barbiturates and carbamazepine as inducers of the liver enzymes. Salicylates, dicoumarol, furosemide in a high dose (250 mg) and clofibrate displace levothyroxine from protein binding, raising the free T4 level. Phenytoin does the same and also speeds up the metabolism of the hormone in the liver. Protease inhibitors (ritonavir, indinavir, lopinavir) call for strict monitoring of the thyroid parameters. Propylthiouracil, glucocorticoids, beta blockers, amiodarone and iodine-containing contrast media inhibit the peripheral conversion of T4 into T3, and amiodarone, because of its high iodine content, is capable of causing both hyperthyroidism and hypothyroidism. In women taking oestrogen-containing contraceptives or postmenopausal hormone replacement therapy, the need for levothyroxine may increase.
Pregnancy and breastfeeding
Treatment with thyroid hormones must not be interrupted, especially during pregnancy and breastfeeding; in pregnancy the need for the medicine may even grow. Experience of use has not revealed a teratogenic effect or a toxic influence on the foetus with the recommended therapeutic doses; however, excessively high doses during pregnancy can affect the development of the foetus and of the child after birth unfavourably.
During lactation levothyroxine is excreted in breast milk, but at therapeutic doses its concentrations are too low to cause hyperthyroidism or suppression of TSH secretion in the child. In pregnancy levothyroxine is not combined with antithyroid agents in the treatment of thyrotoxicosis: adding the hormone would require an increase in the dose of the antithyroid medicine, and that medicine, unlike levothyroxine, crosses the placenta in pharmacologically active amounts and can cause hypothyroidism in the foetus. That is why thyrotoxicosis in pregnant women is treated with antithyroid agents alone. Diagnostic tests with suppression of thyroid function are not carried out during pregnancy: the administration of radioactive substances is contraindicated.
Adverse effects
With a correctly chosen dose and regular monitoring of the clinical and laboratory parameters there should be no undesirable reactions. They appear when the individual tolerance threshold has been exceeded or when the dose is built up too quickly at the start of treatment, and they reproduce the picture of hyperthyroidism.
- of the heart — rhythm disturbances, including atrial fibrillation and extrasystoles, tachycardia, palpitations, anginal pain;
- of the nervous system — headache, tremor, motor restlessness, insomnia, benign intracranial hypertension;
- of the muscles — muscle weakness and muscle cramps;
- general — flushes, a rise in temperature, increased sweating, weight loss;
- of the digestive system — vomiting and diarrhoea;
- of the reproductive system — disturbances of the menstrual cycle;
- in hypersensitivity — allergic reactions, above all of the skin and the respiratory system, including angioedema.
In such cases the daily dose is reduced or the medicine is withdrawn for several days, and once the symptoms have gone treatment is cautiously resumed.
Overdose
An overdose of levothyroxine causes a picture of hyperthyroidism and can lead to acute psychosis, especially in patients at risk of psychotic disorders. A reliable sign of overdose is a rise in the T3 concentration — it is more informative than a rise in T4 or free T4. Symptoms of a marked acceleration of the metabolism appear.
Depending on the degree of the overdose, treatment is interrupted and laboratory tests are carried out. The manifestations of the intense β-sympathomimetic action — tachycardia, restlessness, agitation and hyperkinesia — are eased with beta blockers; in a massive overdose plasmapheresis may help. In sensitive patients, when the individual tolerance threshold is exceeded, isolated cases of seizures have been described, and with many years of levothyroxine abuse, several cases of sudden cardiac death.
How to get a prescription for Euthyrox® N 25 online
Levothyroxine is dispensed on prescription: the dose is chosen from the test results, and changing it without monitoring the TSH can end in either persistent hypothyroidism or drug-induced hyperthyroidism.
During the online consultation the doctor will go through the test results and any concomitant illnesses, will discuss the rules for taking it on an empty stomach and combining it with other medicines and, if there are no contraindications, will issue an electronic prescription — the medicine can be collected from a pharmacy using its code.
